Structured lipid containing gamma-linolenic or dihomogamma-linolenic fatty acid residue, a medium chain (C6-C12) Fatty acid reside and a N-3 fatty acid residue

ABSTRACT

There is disclosed structured lipid containing either a gamma-linolenic acid or a dihomogamma-linolenic acid residue, together with an n-3 fatty acid residue and a medium chain fatty acid residue on the same glycerol backbone. This structured lipid is particularly well adapted to the treatment of disease or stress states. The gamma-linolenic or dihomogamma-linolenic acid residues modify the prostanoid synthesis pathway, reducing the level of series &#34;2&#34; prostanoids and elevating the levels of series &#34;1&#34; and &#34;3&#34; prostanoids. The n-3 fatty acid residue enhances the level of series &#34;1&#34; prostanoids as well as increases the production of series &#34;3&#34; prostanoids. The medium chain fatty acid residues enhances the absorption of the structured lipid. There is also disclosed enteral and parenteral diets as well as nutritional supplements containing the structured lipids of the invention.

This application is a division of application Ser. No. 08/410,581, filedMar. 30, 1995, now U.S. Pat. No. 5,661,180, which is a continuation ofapplication Ser. No. 08/004,828 filed Jan. 15, 1993, abandoned.

TECHNICAL FIELD

The present invention relates to a new structured lipid and a method oftreatment using the structured lipid. The structured lipid and method ofthe invention provide benefits in the treatment of a variety of diseaseand stress states. The structured lipid of this invention consists of aglycerol backbone with at least one gamma linolenic acid (18:3n-6 orGLA) or dihomogamma-linolenic acid (20:3n-6 or DHGLA) residue incombination with a medium chain (C₆ -C₁₂) fatty acid residue and a C₁₈-C₂₂ n-3 fatty acid residue selected from alpha-linolenic (18:3n-3), andstearodonic (18:4n-3), eicosapentaenoic (20:5n-3) and docosahexaenoic(22:6n-3) acid. This structured lipid provides excellent nutritionalsupport, is easily absorbed, and due to the unique proportions of n-3and n-6 fatty acids will modulate the severity of eicosanoid-mediateddiseases by reducing the level of potentially dangerous series "2"prostaglandins and series "4" leukotrienes in patients.

BACKGROUND ART

The term "lipid" generally denotes a heterogeneous group of substances,associated with living systems, which have the common property ofinsolubility in water but solubility in non-polar solvents such ashydrocarbons or alcohols. Included in the group are the oils and fats ofour diet together with the so-called phospholipids associated with cellmembranes. These substances have in common that they are esters oflong-chain fatty acids.

Monocarboxylic, aliphatic fatty acids are the structural componentscommon to most of the lipids that interest food chemists, and many ofthe properties of food lipids can be accounted for directly in terms oftheir component fatty acids. Almost without exception the fatty acidsthat occur in foodstuffs contain an even number of carbon atoms in anunbranched chain, e.g. lauric and dodecanoic acid. Besides the saturatedfatty acids, of which lauric acid is an example, unsaturated fatty acidshaving one, two, or sometimes up to six double bonds are common.

Alpha-linolenic acid (systematically all-cis-9,12,15-octadecatrienoicacid) has the structure:

    CH.sub.3 --CH.sub.2 --CH═CH--CH.sub.2 --CH═CH--CH.sub.2 CH═CH--(CH.sub.2).sub.7 --COOH

Gamma-linolenic acid is a less common isomer with double bonds at the6-, 9- and 12-positions.

The system used for the identification of double-bond positions will beapparent by comparison of the structure with the systematic name. Thestructure of a fatty acid can be indicated by a convenient shorthandform giving the total number of carbon atoms followed by a colon andthen the number of double bonds with the position of the double bondsgiven after the symbol Δ. Thus for example α-linolenic acid would bewritten simply as 18:3Δ9,12,15.

The oils and fats are obviously the lipids that most interest the foodchemist. These consist largely of mixtures of triglycerides, i.e. estersof the trihydric alcohol glycerol (propane-1,2,3-triol), and threefatty-acid residues which may or may not be identical. "Simple"triglyceride molecules have three identical fatty-acid residues while"mixed" triglycerides have more than one species of fatty acid. Thus anaturally occurring fat will be a mixture of quite a large number ofmixed and simple triglycerides. It is important to remember thatorganisms achieve a desirable pattern of physical properties for thelipids of, for example, their cell membranes or adipose tissue byutilizing an appropriate, and possibly unique, mixture of a number ofdifferent molecular species, rather than by utilizing a single molecularspecies which alone has the desired properties, as is the usual tacticwith proteins and carbohydrates.

Fats and oils can be viewed in terms of their component triglycerides.The first descriptions of the glyceride structure of fats assumed thatall their component triglycerides were simple. Thus a fat containingpalmitic (hexadecanoic), stearic (octadecanoic), and oleic(cis-octadec-9-enoic) acids would be a mixture of the three triglyceridespecies tripalmitin, tristearin, and triolein. The first attempts toseparate the component glycerides of fats, by the laborious process offractional crystallization from acetone solutions at low temperatures,made it clear that much greater numbers of species of triglyceridesoccurred than would be expected from this simple concept. Fats and oilsbecame recognized as clearly defined mixtures of mixed and simpletriglycerides.

The fatty acids, in the form of the triglycerides of the dietary fatsand oils, provide a major proportion of our energy requirements as wellas, when in excess, contribute to the unwelcome burden of superfluousadipose tissue that so many of us carry. In recent years we have begunto appreciate that certain dietary fatty acids have a more particularfunction in human nutrition. Rats fed a totally fat-free diet show awide range of acute symptoms affecting the skin, vascular system,reproductive organs, and lipid metabolism. Although no correspondingdisease state has ever been recorded in a human patient, similar skindisorders have occurred in children subjected to a fat-free diet. Thesymptoms in rats could be eliminated by feeding linoleic or arachidonicacids (which in consequence became known for a time as vitamin F), andit is generally accepted that 2-10 g of linoleic acid per day will meetan adult human's requirements.

The identification of these two "essential fatty acids" in the 1930spreceded by some 25 years their identification as precursors of a groupof animal hormones, the eicosanoids. Although animal tissues are unableto synthesize either of these two fatty acids, they readily convert theC₁₈ acid to the C₂₀ acid.

The many different eicosanoids all have similar structures. The reasonsfor the stringent requirements for the positions of the double bonds inessential fatty acids are clearly evident from the biosynthesis ofprostaglandin E₂ from linoleic acid.

Other eicosanoids vary in the degree of reduction of the ring oxygensand presence of double bonds in the chain. Details of their numerousphysiological activities are still accumulating in the scientificliterature, but they are best known for their involvement ininflammation and the contraction of smooth muscle.

There are indications from studies of Eskimos that it is the high levelsin their diets of certain polyunsaturated fatty acids (n-3 fatty acidswhich are abundant in fish oils) that are responsible for the remarkablylow incidence of arterial disease in a population that appears to breakall the usual nutritional rules. Fish oils are rich in fatty acids suchas eicosapentaenoic acid (20:5Δ all cis-5,8,11,14,17) anddocosahexaenoic acid (22:6Δ all cis-4,7,10,13,16,19). As seen from theirstructural formulae, these fatty acids are characterized by having adouble bond in the n-3-position, i.e. at the third carbon atom whencounting from the methyl end of the hydrocarbon chain. The nomenclatureof n-3 is equivalent to the old ω-3 designation. This means that a quitedistinct set of eicosanoids are derived from them compared with thosefrom the so-called n-6-series. Prostaglandins synthesized from n-6 fattyacids are generally more active than those from n-3-fatty acids inpromoting the formation of the blood clots that are involved inthrombosis. It remains to be seen whether these observations will leadto useful modifications of our diet or to changes in clinical practice.

For many years, it has been known that levels of thromboxane A₂,prostacyclin and PGE₂ (collectively "series 2 prostanoids") are elevatedin endotoxemia and play a crucial role in septic and endotoxic shock,particularly in endotoxic shock caused by lipopolysaccharides fromgram-negative bacteria such as E. coli. These same metabolites (series 2prostanoids) have been shown to increase in a variety of other diseaseand stress states. Moreover, there is an imbalance between series-1 andseries-2 prostaglandins in disease states such that the harmful series-2prostaglandins predominate. Series 2 prostaglandins are formed fromarachidonic acid (20:4n-6) which is derived from the n-6 fatty acidlinoleic acid (18:2n-6) by enzymatic desaturation and elongationreactions.

Leukotriene B₄ (LTB₄) is a metabolite of arachidonic acid formed via alipooxygenase enzyme. LTB₄ is a potent chemotactic agent for neutrophilsand has been shown to stimulate neutrophils to secrete large quantitiesof potentially injurious mediators in inflammatory diseases. The use ofn-3 fatty acids will regulate the intensity of n-6 prostaglandins andleukotriene biosynthesis since excess eicosanoid production can causepathophysiology.

In the last few years, there have been a number of attempts to alter therelative supply of dietary n-3/n-6 fatty acids to modify the eicosanoidsynthesis pathway and shift the proportions of series 1, series 2 andseries 3 eicosanoids to produce a more desirable health status. It isknown that both n-3 and n-6 types of fatty acids can be metabolicallyelongated and desaturated, however, the body cannot change the positionof the double bonds; therefore, n-3 fatty acids cannot be converted ton-6 fatty acids and visa versa. Since each type of eicosanoid comes froma different family of fatty acids (e.g., n-3, n-6, n-9), dietmodification is a promising course to modulate tissue eicosanoidbiosynthesis.

U.S. Pat. No. 4,752,618 ("'618 Patent"), issued Jun. 21, 1988, thedisclosure which is incorporated herein by reference, was one of theearliest references which discloses diet modification for treatment ofdisease. The '618 Patent describes the treatment of infection inpatients through reducing the amount of n-6 fatty acids in the diet(particularly reduction of linoleic acid) by replacing a portion of then-6 fatty acids with n-3 fatty acids. The optimum source of n-3 fattyacids disclosed in the '618 Patent is fish oil, e.g., menhaden oil. Thisdietary modification leads to the production of a larger proportion ofseries "3" prostanoids in place of series "2" prostanoids than normallyis obtained from standard diets. Although the series "3" prostanoids,and the attendant reduction of series "2" prostanoids, has substantialbeneficial effects, in some circumstances, particularly in the treatmentof endotoxic shock, replacement of series "2" prostanoids with series"1" rather than the series "3" prostanoids might be even morebeneficial. Series "1" prostanoids have already been shown to provide acertain amount of protection in endotoxic lung injury and traumaticshock.

The synthesis path for forming the series "1" prostanoids is fromlinoleic acid (18:2n6) to gamma-linolenic acid (18:3n6 or GLA) todihomogamma-linolenic acid (20:3n6) to the series "1" prostanoids.

The following represents the metabolic pathway of linoleic acid toseries "1" and "2" prostaglandins. ##STR1##

Dihomogamma-linolenic acid competes with arachidonic acid (20:4n6), forthe enzyme cyclooxygenase. Cyclooxygenase is a critical enzyme in theformation of both the series "1" and series "2" prostanoids. When GLA isformed endogenously substantially all the gamma-linolenic acid is madeinto arachidonic acid, the precursor of the series "2" prostanoids.Accordingly, one could modify the diet to contain relatively high levelsof gamma-linolenic acid in order to skew the prostanoid synthesispathway to preferentially increase the production of series "1"prostanoids.

In a paper by Hirschberg et al., "The Response to Endotoxin in GuineaPigs After Intravenous Blackcurrant Seed Oil," Lipids 25, 491-496 (1990)it is disclosed that high levels of blackcurrant seed oil, an oil richin gamma-linolenic acid, was supplied as part of a parenteral diet toguinea pigs, who were then challenged with endotoxin. The results weresomewhat disheartening; the gamma-linolenic acid provided no betterprotection (and possible worse systemic results) against endotoxin shockthan did the classic lipid diet with soybean oil, a diet high inlinoleic acid.

However, a recent study by Karlstad et al. JPEN 1992; 16(1):215disclosed the measurement of the levels of dihomogamma-linolenic acid inthe blood after the addition of 0, 2.7%, 4.4% and 6.1% gamma-linolenicacid to a parenteral diet. The authors found that for 4.4% and 6.1%gamma-linolenic acid enrichment, there was a 4-5 fold increase in theplasma dihomogamma-linolenic/arachidonate ratio. The increase in plasmadihomogamma-linolenic acid should lead to the production of more series"1" prostanoids.

The results of the Karlstad et al. and Hirschberg studies can beinterpreted to mean that, beyond a certain level, dietarygamma-linolenic acid is not utilized properly. It may be that excessgamma-linolenic acid may be formed into arachidonic acid, leading toseries "2" prostanoid buildup. Accordingly, one problem is how toachieve a higher level of dihomogamma-linolenic acid in plasma andtissues without parallel buildup of arachidonic acid.

It has been theorized that a structured lipid containing a medium chainfatty (C₆ -C₁₂) acid residue may provide improved absorption of otherfatty acids attached to the structured lipid. A recent paper by JensenA.J.C.N. Suppl. no. 62; 1992 disclosed that a structured lipidcontaining medium chain fatty acid residues and long chain fatty acidresidues (n-3 fatty acids from fish oil) are absorbed faster by the bodythan the physical mixture of the same fatty acids. There is nosuggestion or teaching that a specific structured lipid would be usefulto modify the prostanoid synthesis pathway.

U.S. Pat. No. 4,906,664 discloses a method of treating patients withcancer through administering a diet containing a structured lipid of theformula: ##STR2## where one of R₁, R₂ and R₃ is a medium-chain fattyacid, and a second one of R₁, R₂ and R₃ is an ω fatty acid, and thethird one of R₁, R₂ and R₃ is selected from the group consisting ofhydrogen, hydroxyl, short, medium and long-chain fatty acids. Thisreference does not suggest or disclose the specific structured lipid ofthe instant application.

European Patent Application Number 87114297.2 discloses a triglyceridehaving a C₈ to C₁₄ fatty acid residue at the 2-position of thetriglyceride and a residue of C₁₈ or higher fatty acids at the 1 and 3position thereof. There is no suggestion or disclosure of the specificstructured lipids of the instant invention nor the benefits that can berealized by feeding the structured lipids of this invention.

International Application No. PCT/DK 89/00239 filed Oct. 10, 1989discloses the triglycerides 2-docosahexaenoyl!-1,3-di(octanoyl/decanoyl) glycerol for nutritionalcompositions for enteral or parenteral purposes, especially as breastmilk replacers.

International Application No. PCT/DK 89/00237 filed Oct. 10, 1989discloses the triglycerides 2-arachidoyl-1,3-di(octanoyl/deconoyl)glycerol and the use of these materials in nutritional products.

International Application Number PCT/US89/01364 with a publicationnumber of WO 89/09596 discloses a transesterification product of amixture of fatty acids and triglycerides which include dairy fat as aprimary component. A method of nutritional support using thiscomposition is also disclosed.

International Application Number EP 421,867 discloses the production ofstructured lipids enriched in gamma-linolenic and/or stearidonic fattyacids. The process comprises hydrolysing a mixture of glycerides or thefatty material containing them with a lipase having specificity such asnot to hydrolyse the ester bond of the gamma-linolenic and stearidonicfatty acids esterified in position 1, 2 or 3 and recovering thenon-hydrolysed residue from the enzymatic reaction by separating thefatty acids produced.

Canadian Patent Application 2000391 with a WPI Accession Number of90-139962/19 discloses the triglyceride2-(alpha-linolenoyl)/gamma-linolenoyl)-1,3-di (octanoyol/decanoyl)glycerol as useful in nutritional compositions. It is suggested thatthese triglycerides are useful as components in nutritionalcompositions. The fatty acids are essential for control of tonus ofsmooth-muscle cells in the blood vessels or the tonus of the smoothmuscle cells in the lungs and thus are useful in the control ofrespiratory distress. This reference does not suggest or disclose thespecific structured lipids of this invention nor the methods of usingthem.

U.S. Pat. No. 4,528,197 discloses a method of enhancing proteinanabolism in a hypercatabolic mammal, the method comprising parenterallyadministering an emulsion of triglycerides which, on hydrolysis, yieldsboth long chain fatty acids and medium chain fatty acids.

U.S. Pat. No. 4,871,768 discloses a synthetic triglyceride comprising aglycerol backbone having three fatty acids attached thereto, said fattyacids being selected from a first group consisting of ω-3 fatty acids,and a second group consisting of caprylic acid, capric acid and mixturesthereof. This patent also discloses a method for minimizing the effectsof infection and minimizing the effects of subsequent infection byadministering a diet containing 10 to 80% by weight of an oily fraction,said oily fraction being the aforementioned fatty acid.

U.S. Pat. No. 4,701,469 discloses triglycerides of the formula. ##STR3##wherein R represents an acyl fragment of a polyunsaturated fatty acidcontaining 18 to 22 carbon atoms, the acyl fragment being capable ofbeing oxidized, however, R cannot represent the acyl fragment ofeicosatetrayn-5, 8, 11, 14-oic acid, and wherein n represents an integervarying from 2 to 16; a process for their preparation, their dieteticand therapeutic applications and compositions containing them.

None of these references either suggest or disclose a structured lipidof the formula: ##STR4## wherein

(1) at least one of R₁,R₂ or R₃ is a fatty acid residue esterified toglycerol and selected from the group consisting of gamma-linolenic acid,dihomogamma-linolenic acid, and active derivatives thereof;

(2) a second of R₁, R₂ or R₃ is a fatty acid residue esterified toglycerol and selected from the group consisting of C₁₈ -C₂₂ n-3 fattyacids and C₆ -C₁₂ fatty acids and active derivatives thereof; and

(3) a third of R₁,R₂ or R₃ is a fatty acid residue esterified toglycerol and selected from the group consisting of C₆ -C₁₂ fatty acidsand active derivatives thereof.

Further, these references fail to suggest or disclose a method ofmodulating metabolic response to trauma and disease states in patientsthrough administering the structured lipid of this invention.

One benefit of this invention over the prior art is that a structuredlipid containing a GLA or DHGLA residue and a medium chain fatty acidresidue (C₆ -C₁₂) will increase the incorporation of the GLA or DHGLAinto tissues and thereby beneficially modify eicosanoid biosynthesis.Medium chain fatty acids in the structured lipid also provide additionalfat calories and increase the absorption and clearance of the structuredlipid so that the reticuloendothelial system is not blocked with anoverabundance of long chain triglycerides. More importantly, mediumchain fatty acids do not act as substrates for eicosanoid synthesis.Accordingly, one aspect of the present invention is concerned with astructured lipid which modifies eicosanoid synthesis in a positivemanner to produce more series "1" eicosanoids. Another aspect of theinvention relates to a physical blend of structured lipids. The firststructured lipid contains gamma-linolenic acid and/ordihomogamma-linolenic acid and C₆ -C₁₂ fatty acid residues and a secondstructured lipid which contains n-3 fatty acid residues and C₆ -C₁₂fatty acid residues.

An additional aspect of the invention is to provide a method of treatingdisease and stress states using the specific structured lipid of theinvention. These and other features of the invention will be apparentfrom the following description and the claims.

DISCLOSURE OF THE INVENTION

The present invention features a new family of structured lipids to beused in enteral and parenteral nutritionals, and a method of modulatingthe metabolic response to trauma and disease using the structured lipidsof the invention. The structured lipids of the invention provideparticular benefits for modification of the prostanoid synthesispathway.

There is disclosed a structured lipid having the structural formula:##STR5##

wherein:

1) at least one of R₁,R₂ or R₃ is a fatty acid residue which isesterified to glycerol and selected from the group consisting ofgamma-linolenic acid, dihomogamma-linolenic acid and active derivativesthereof;

2) a second of R₁,R₂ or R₃ is a fatty acid residue which is esterifiedto glycerol and selected from the group consisting of C₁₈ -C₂₂ n-3 fattyacids, C₆ -C₁₂ fatty acids and active derivatives thereof; and

3) the third of R₁,R₂ or R₃ is a fatty acid residue which is esterifiedto glycerol and is selected from the group consisting of C₆ -C₁₂ fattyacids and active derivatives thereof.

The term "active derivatives", as used herein includes esters, ethers,amines, amides, substituted fatty acids (e.g., halogen substituted fattyacids), and other substitutions which do not affect the beneficialproperties of the structured lipid. The structured lipid of thisinvention must contain either a gamma-linolenic acid ordihomogamma-linolenic acid residue, a C₁₈ -C₂₂ n-3 fatty acid residueand a C₆ -C₁₂ residue. In an alternative embodiment a physical mixtureof two structured lipids is disclosed wherein the first structured lipidcontains a GLA and/or DHGLA fatty acid residue and a medium-chain fattyacid residue and the second structured lipid contains medium-chain fattyacid residues and n-3 fatty acid residues.

A preferred structured lipid of the invention has a medium chain (C₆-C₁₂) fatty acid residue in the 2 position, a gamma-linolenic acid orDHGLA residue at 1 or 3 and a 20:5n-3 at 1 or 3.

The C₁₈ -C₂₂ n-3 fatty acids useful in this invention are:alpha-linolenic (18:3n-3), stearidonic (18:4n-3), eicosapentaenoic(20:5n-3) and docosahexanoic (22:6n-3). The C₆ -C₁₂ fatty acids usefulin this invention are caproic, caprylic, capric, and lauric.

The invention also features an enteral or parenteral preparationcontaining specific structured lipids that are prepared from a physicalblend of oils. This oil blend is 10-90% by weight an oil which is 5-70%by weight C₁₈ -C₂₂ n-3 fatty acids, and 10-90% of a second oil having5-70% of fatty acids selected from gamma-linolenic acid and/ordihomogamma-linolenic acid and 10-90% of a third oil which is at least50% by weight medium chain (C₆ -C₁₂) fatty acid residues. This mixturemay then be subjected to a transesterification reaction to yield areaction product that contains the structured lipids of this invention.

The invention further features an enteral or parenteral nutrition whichcontains at least two structured lipids of this invention. Thiscombination of structured lipids consists of a first structured lipidcontaining gamma-linolenic and/or dihomogamma-linolenic acid residuesand C₆ -C₁₂ fatty acid residues, and active derivatives thereof; thesecond structured lipid consists of C₁₈ -C₂₂ n-3 fatty acid residues andC₆ -C₁₂ fatty acid residues and active derivatives thereof.

Another aspect of the invention is a method of modulating the metabolicresponse to trauma and disease states in patients by administering adietary supplement or a complete nutritional containing a structuredlipid of the invention. This method is particularly pertinent where thetrauma and disease states are caused by burns, immune disorders,cardiogenic shock, sepsis, endotoxemia, bacteremia, cancer, chronicobstructive pulmonary diseases, pediatric and adult respiratory distresssyndrome, severe inflammatory diseases such as ulcerative colitis,regional enteritis, pancreatitis and atherosclerosis. The dietarysupplement or complete nutritional of the invention modulates or reducesthe level of series "2" prostanoids and may be administered eitherenterally or parenterally. If administered parenterally, it ispreferably administered as part of a total parenteral diet.

These aspects of the invention will be more fully elucidated in thefollowing detailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The structured lipids of the present invention provide substantialbenefits in terms of modifying the prostanoid synthesis pathway,resulting in an improved response to endotoxic shock and other stressstates. These dietary supplements will have particular advantageousresults when used enterally.

The invention is used in enteral or parenteral nutrition where 5-75% ofthe calories included in the total diet are taken as fat or lipid. Ifthe nutrition is administered parenterally, the diet is 1-40% by weightas an emulsion of the lipids according to the invention, most preferablyat 5-30% by weight. When taken enterally, the lipids according to theinvention may be mixed into a complete or incomplete food which suppliesother essential nutrients and fats or it may be in the form of a200-1500 mg capsule.

The use of a structured lipid having both gamma-linolenic acid (ordihomogamma-linolenic acid) and a long-chain polyunsaturated n-3 fattyacid will provide particular benefits to the stressed or otherwisecompromised patient. By providing these fatty acids on the samestructured lipid, they are presented to the tissue simultaneously. Thelong-chain polyunsaturated n-3 fatty acid will serve to minimize theelongation of gamma-linolenic acid to arachidonic acid, yielding abetter dihomogamma-linolenic acid/arachidonic acid ratio and a shiftaway from series "2" prostanoid synthesis toward series 1. Since theseries "2" prostanoids are pro-inflammatory while the series "1"prostanoids appear to have some beneficial effects in treatinginflammation, this will improve the response to endotoxin challenge.Further, the inclusion of the n-3 fatty acids, particularlyeicosapentaenoic acid, decreases the oxygenation of arachidonic acid, bycompeting for binding sites on cyclooxygenase to yield some series "3"prostanoids. As shown in the '618 Patent, the shift from series "2" toseries "3" prostanoids also has beneficial effects in treatinginfection.

The inclusion of C₆ -C₁₂ fatty acid residues in the structured lipidwill also have additional benefits. The C₆ -C₁₂ fatty acid residuesimprove intestinal absorption and direct the structured lipid throughthe lymphatic rather than the portal pathway, leading to more effectiveabsorption into the systemic circulation. Since higher levels ofstructured lipid can be absorbed than the physical mixture, (See Jensenet al., previously cited), the structured lipid is a more effectivemeans of delivering the gamma-linolenic acid or dihomogamma-linolenicacid and n-3 fatty acids to the desired location.

Oils rich in gamma-linolenic acid include evening primrose oil which isabout 9% GLA by weight, borage oil which is about 25% and black currantseed oil which has about 15%. Other sources of GLA and DHGLA useful inthe preparation of the structured lipids of this invention include algaeand fungal oils. Oils rich in n-3 fatty acids include most fish oils, inparticular menhaden oil which is approximately 22% by weight and certainfruit and vegetable oil such as canola oil which is approximately 10% byweight. Medium chain triglycerides are available primarily by thefractionation of palm kernel oils or coconut oils.

The structured lipid of the invention may be made by any procedurecommonly used to make structured lipids generally. For example, aninteresterification or transesterification reaction made by mixing oils,or selective fractions of the oils, in stoichiometric proportions andthen causing the transesterfication reaction to proceed using catalystsor enzymes could be used. In the alternative, certain companies havediscussed the possibility of making specific "designer oils". Thesecompanies include Novo-Nordisk Industries A/S which claims to have anenzymatic procedure to direct the synthesis of specific structuredlipids. Other companies use different modifications of standardprocedures. However, although a standard transesterfication proceduremay result in a mixture of the structured lipids of the invention plusother oils, this mixture is intended to be included within the claims,so long as efficacious amounts of the structured lipids of the inventionare present.

The following examples using high fat enteral diets still furtherelucidate the advantages of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION EXAMPLE I

In this example, the substitution of the n-3 fatty acid eicosapentaenoicacid (EPA; 20:5n-3) or a combination of EPA and gamma-linolenic acid(GLA 18:3n6) for linoleic acid (LA; 18:2n-6) in a diet was investigated.Three groups of pigs were fed isocaloric and isonitrogenous diets foreight days. The diets contained 55% of the calories from either corn oil(an oil containing a large percentage of LA) which was Diet A; fish oil(an oil containing a large percentage of EPA) which was Diet B; or acombination of fish oil and borage oil (a diet containing the blend ofEPA and GLA) which was Diet C. All feeding was enteral.

At the end of the eight day feeding period, acute lung injury wasinduced with intravenous E. coli endotoxin. Cardiopulmonary parameters,specifically systemic and pulmonary arterial pressures and arterialblood gases, and cardiac output, were measured and compared.

All of the pigs showed a fall in PaO₂ but the EPA and EPA/GLA dietsprovide substantially equal attenuation in the fall. Similarly, both theEPA and EPA plus GLA diets were better than the LA diet in terms ofattenuating the early rise in pulmonary vascular resistance followingendotoxin challenge. Following endotoxin infusion, pulmonary vascularresistance (PVR) increased markedly at 20 minutes (Early Phase Response)in the group of pigs fed diet A. At one hour PVR had decreased butremained higher than that observed at 0-time. PVR steadily increasedover the next 2 hours and appeared to stabilize between the third andfourth hour (Late Phase Response). The pigs fed diet B did notdemonstrate the Early Phase Response to endotoxin infusion, but the LatePhase Response was substantially identical to that observed in the groupfed diet B. Feeding pigs diet C also abolished the Early Phase Responseto endotoxin infusion, but appeared to attenuate the late phaseresponse. However, the cardiac output of the pigs which had EPA plus GLAwas much closer to the baseline levels than either the EPA diet or theLA diet. Accordingly, it is clear that the combination of EPA and GLAprovides improvement in treating endotoxic shock and the associatedcatabolic stress state.

EXAMPLE II

The pathogenesis of adult respiratory distress syndrome ismultifactorial and because of the complicated disease process it hasbeen difficult to model in animals. In man, the injury often becomespresent with several insults, such as shock and secondary infection,whereas usually only a single insult is tested in animal models. Becauseof the association between burn injury and sepsis, an animal model hasbeen developed that is clinically relevant to adult respiratory distresssyndrome. In the animal model of burn and endotoxin injury, rats areanesthetized and then burned with boiling water on their dorsum toproduce a 30% body surface area full-thickness skin lesion. This causesa short-term shocklike syndrome characterized by transient hypotensionwhich is treated with fluid resuscitation. Following resuscitation,there is an increase in energy expenditure and a negative nitrogenbalance due to protein wasting for many days. Three days after creatingthe burn injury and during the hypermetabolic phase, a 10 mg/kg dose ofendotoxin was injected intravenously to mimic the clinical developmentof sepsis in burned patients.

Twenty male Long-Evans rats (250 g) are randomly divided into twotreatment groups of equal number. The jugular vein is cannulated (0.025"I.D.×0.047" O.D.) for blood sampling and infusions. An intragastriccatheter is surgically implanted into the stomach and passed into theduodenum for enteral feeding. Catheters are exteriorized at themid-scapular region, tunneled through a protective spring and attachedto an infusion swivel that allows for free movement by the rat. Whileunder anesthesia, a 30% (body surface area) third-degree burn injury isproduced by immersing the shaven dorsal surface through a preformed moldin a 90-95° C. waterbath for 15 seconds. The rats are fluid resuscitatedwith an intraperitoneal injection of sterile lactated Ringers (2.5ml/100 g body wt) and a 4 hour intravenous infusion of 0.9% saline (2.5ml/hr). This resuscitation procedure ensures 100% survival of burnedrats. The rats are housed individually in metabolic cages and allowedwater ad libitum.

After burn trauma, the rats are enterally fed for 72 hours. Group I(n=10) receives an intragastric infusion of a corn oil based diet (seeTables 1 and 2; Diet A) and group II (n=10) receives a structured lipiddiet (see Tables 1 and 2; Diet B) for 72 hours after the burn injury.Following this 72 hour period, the rats are anesthetized withpentobarbital (30 mg/kg) and the femoral artery is cannulated and abaseline blood sample (0.5 mL) is taken for blood gas and hematologydeterminations. Tissue blood flow is determined by radiolabelledmicrospheres and arterial blood pressure is monitored. Blood samples aredrawn for analysis of eicosanoids (PGE₂, PGI₂, 6-keto-PGF₁ alpha, TXB₂and LTB₄) and platelet aggregation studies.

                  TABLE 1    ______________________________________    COMPOSITION OF THE OIL BLEND FOR THE EXPERIMENTAL    DIETS                   WEIGHT %    OIL              DIET A  DIET B    ______________________________________    Corn             100      0    MCT              0       60    Concentrated fish                     0       20    Borage           0       20    ______________________________________

                  TABLE 2    ______________________________________    FATTY ACID PROFILES FOR THE EXPERIMENTAL DIETS                       % OF TOTAL BY WEIGHT    FATTY ACID        DIET A       DIET B    ______________________________________    Caprylic (8:0)    0.0          38.4    Capric (10:0)     0.0          21.3    Palmitic (16:0)   10.9         4.4    Oleic acid (18:1n9)                      25.2         4.5    Linoleic acid (18:2n6)                      59.4         7.5    Gamma-linolenic acid (18:3n6)                      0.0          4.6    Alpha-linolenic acid (18:3n3)                      1.4          0.20    Eicosapentaenoic acid (20:5n3)                      0.0          5.0    Docosahexaenoic acid (22:6n3)                      0.0          2.5    Others*           3.1          11.6    n-6/n-3 ratio     43.2         1.4    ______________________________________     *Fatty acids less than 1.8% of total fatty acids.

Lung microvascular permeability and radioactive lung:heart ratios aredetermined by the localization rate of ^(99m) -Human Serum Albumin (HSA)in the lungs by gamma-scintigraphy. An intravenous injection of 0.2 mL^(99m) -TC-HSA (500-600 μCi) is given to each rat and 20 minutes later ascintigraphic recording is taken using a computerized gammascintillation camera to determine baseline lung microvascularpermeability. Fifteen minutes later the rats are given an intravenousinjection of 10 mg/kg Salmonella enteritidis endotoxin to model thedevelopment of sepsis in burned patients. Four hours after endotoxininjection a second injection of 0.2 mL ⁹⁹ TC-HSA (500-600 μCi) is givenand scintigraphic recordings are taken for 1 hour. Finally, a 0.4 mLintravenous injection of ⁹⁹ TC-macroaggregrated albumin (500-900 μCi) isused to highlight the left and right lungs by gamma scintigraphy.

Bronchoalveolar lavage cellular analysis is a valuable technique forassessing the inflammatory and immune effector cells present in thelungs of patients. The total and differential cell counts are used inthe assessment of the inflammatory response and for predicting diseaseactivity and response to therapy. Bronchoalveolar lavage is performed inanesthetized rats after cannulation of the trachea with tubing attachedto a 12 mL syringe containing saline. The abdominal cavity is opened bymidline laparotomy and a terminal blood sample (4 mL) is taken from theabdominal aorta. Arterial blood PCO₂, PO₂, and pH is determined using ablood gas analyzer. A total leukocyte (WBC), differential and plateletcount is performed on the blood samples. The total WBC and plateletcount is performed on a hemacytometer. Bronchoalveolar lavage fluid isanalyzed for eicosanoids and differential cell counts. Total proteincontent of bronchoalveolar lavage fluid is measured by a modified Lowrytechnique.

Results from this study will provide convincing evidence on thephysiological and clinical effect of the structured lipids disclosed inthis invention. Parenteral or enteral administration of structured lipidof this invention will improve survival rate and reduce arterialhypoxemia, pulmonary edema, and systemic hypotension inendotoxin-challenged burned rats. Nutritional support with structuredlipids of this invention decreases neutrophil infiltration andaccumulation in the lung and protects against endotoxin-inducedinterstitial edema and lung weight gain and reduces the pulmonaryvascular permeability and rate of albumin leak thus protecting againstacute lung injury. The experimental evidence will also demonstrate thatthe structured lipids of the present invention will reduce neutrophilactivation since there is a decrease in lung myeloperoxidase contentafter a septic challenge. This will protect against the development ofacute lung injury since activated neutrophils release myeloperoxidasewhich will interact with superoxide derivatives to form hypochlorousacid and free chlorine and produce severe damage to the vascularendothelium, mitochondria and collagen. Enteral or parenteral nutritionwith structured lipids of this invention will decrease blood levels ofPGE₂, a detrimental pro-inflammatory series "2" prostaglandin, andincrease PGI₁, a beneficial antiinflammatory series "1" prostaglandin.

Structured lipids according to the invention decrease the level ofthromboxane A₂, increase the level of prostacyclin, decrease plateletaggregation, improve tissue blood flow and hemodynamics which offersprotection against endotoxic and septic shock. Structured lipids of theinvention will reduce neutrophil accumulation in lung and LTB₄ levels inbronchoalveolar fluid obtained during the early stages ofendotoxin-induced acute lung inflammation. LTB₄ is a metabolite ofarachidonic acid that has potent chemotactic activity for neutrophilsand is responsible for the recruitment and accumulation of neutrophilsin the lung. The decrease in LTB₄ is closely related to decreases inneutrophil recruitment in the lungs of endotoxin-challenged burned rats.Structured lipids of the invention will increase the incorporation ofn-3 fatty acids and decrease the ratio of n-6 to n-3 fatty acids inmembrane phospholipids of alveolar and peritoneal macrophages and lungand liver. In vitro studies of the effects of endotoxin on alveolarmacrophages showed that structured lipids of the invention reduce thebiosynthesis of harmful series-"2" prostaglandins and leukotrienes(LTB₄).

INDUSTRIAL APPLICABILITY

The foregoing examples are merely illustrative and are not intended tobe limiting to the scope of the invention. The medical community haslong sought a nutritional product or supplement that favors ananti-inflammatory, vasodilatory state with less platelet aggregation.The novel lipids of this invention meet these goals by placing on theglycerol backbone residues of GLA or DHGLA, MCT and n-3 fatty acids. Theinvention is described by the following claims.

We claim:
 1. A structured lipid having the formula: ##STR6## in whichR₁, R₂ and R₃ are fatty acid residues esterified to a glycerol backbone,and wherein(a) a first one of fatty acid residues R₁, R₂ and R₃ isselected from the group consisting of gamma-linolenic acid,dihomogamma-linolenic acid and active derivatives thereof; (b) a secondone of fatty acid residues R₁, R₂ and R₃ is selected from the groupconsisting of C₁₈ -C₂₂ n-₃ fatty acids and active derivatives thereof;and (c) a third one of fatty acid residues R₁, R₂ and R₃ is selectedfrom the group consisting of C₆ -C₁₂ fatty acids and active derivativesthereof.
 2. The structured lipid of claim 1 wherein the fatty acidresidue R₂ consists of gamma-linolenic acid, dihomogamma-linolenic acidor active derivatives thereof.
 3. The structured lipid of claim 1wherein the fatty acid residue R₂ consists of consisting of C₁₈ -C₂₂ n-₃fatty acids or active derivatives thereof.
 4. The structured lipid ofclaim 1 wherein the fatty acid residue R₂ consists of C₆ -C₁₂ fattyacids or active derivatives thereof.
 5. A structured lipid according toclaim 1 in which:a) R₁ is gamma-linolenic acid; b) R₂ is caprylic acid,and; c) R₃ is eicosapentaenoic acid.
 6. The structured lipid of claim 1wherein said C₁₈ -C₂₂ n-3 fatty acid is selected from the groupconsisting of alpha-linolenic, stearidonic, eicosapentaenoic anddocosahexaenoic.
 7. The structured lipid according to claim 1 in whichsaid n-3 fatty acid is alpha-linolenic.
 8. The structured lipidaccording to claim 1 in which said n-3 fatty acid is stearidonic.
 9. Thestructured lipid according to claim 1 in which said n-3 fatty acid iseicosapentaenoic.
 10. The structured lipid according to claim 1 in whichsaid n-3 fatty acid is docosahexaenoic.
 11. The structured lipidaccording to claim 1 in which said first one of said fatty acid residueR₁, R₂, and R₃ is gamma-linolenic acid.
 12. The structured lipidaccording to claim 1 in which said first one of said fatty acid residueR₁, R₂, and R₃ is dihomogamma-linolenic acid.
 13. The structured lipidaccording to claim 1 in which said C₆ -C₁₂ fatty acid is selected fromthe group consisting of caproic, caprylic, capric, and lauric.
 14. Thestructured lipid according to claim 1 in which said C₆ -C₁₂ fatty acidis caproic.
 15. The structured lipid according to claim 1 in which saidC₆ -C₁₂ fatty acid is caprylic.
 16. The structured lipid according toclaim 1 in which said C₆ -C₁₂ fatty acid is capric.
 17. The structuredlipid according to claim 1 in which said C₆ -C₁₂ fatty acid is lauric.18. The structured lipid according to claim 1 in which:a) R₁ iseicosapentaenoic acid; b) R₂ is a C₆ -C₁₂ fatty acid, and; c) R₃ isgamma-linolenic acid.
 19. The structured lipid according to claim 1 inwhich:a) said first one of said fatty acid residues R₁, R₂, and R₃ isgamma-linolenic acid; b) said second one of said fatty acid residues R₁,R₂, and R₃ is eicosapentaenoic acid, and; c) said third one of saidfatty acid residues R₁, R₂, and R₃ is a C₆ -C₁₂ fatty acid.
 20. Thestructured lipid of claim 19 wherein one fatty acid residue is agamma-linolenic-acid or dihomogamma-linolenic acid residue, the secondfatty acid residue is a C₆ -C₁₂ fatty acid residue, and the third fattyacid residue is a C₁₈ -C₂₂ n-3 fatty acid residue.